Plasma chambers are often used to generate a plasma. Ions from this plasma are then extracted from the plasma chamber through an aperture to form an ion beam. This plasma may be generated in various ways. In one embodiment, an antenna is disposed outside the plasma chamber, proximate to a dielectric window. The antenna is then excited using an RF power supply. The electromagnetic energy generated by the antenna then passes through the dielectric window to excite feed gas disposed within the plasma chamber.
In another embodiment, the antennas may be disposed within the plasma chamber, and may be referred to as internal antennas. Like the previous embodiment, an RF power supply is electrically coupled to the internal antennas. These internal antennas may include an outer tube, which may be quartz or another dielectric material. An electrically conductive coil is disposed within and usually spaced apart from the outer tube. The RF power supply is electrically coupled to the coil, which emits electromagnetic energy through the outer tube, generating a plasma within the plasma chamber.
However, the plasma that is generated may not be of the desired uniformity throughout the plasma chamber. For example, the plasma density may be greater near the internal antenna and may be reduced in regions away from the internal antenna.
This plasma non-uniformity may affect the extracted ion beam. For example, rather than extracting an ion beam having a constant ion density across its width, the ion beam may have a greater concentration of ions in a first portion, such as near the center, than a second portion, such as at its ends. In other embodiments, it may be desirable to create an ion beam having a known non-uniformity.
Therefore, it would be beneficial if there were an improved system for generating a plasma using a plasma chamber. More particularly, it would be advantageous to improve the plasma uniformity in plasma chambers where internal antennas are employed.